Prediction of optical radiation-induced damage of white paper in cultural heritage preservation

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Light exposure is one pressing preservation issue in all museums, archives and libraries where paper objects undergo ever-increasing cycles of public exhibition and loans. Irreplaceable drawings, prints, documents and books are repeatedly requested. Planning exhibition horizons for paper objects depends fundamentally on light dose decisions. They must balance current display interests against the long-term preservation commitment to prolong the objects’ useful lifespan. For two-dimensional paper objects, useful lifespan is determined significantly by their contrast and color as the only readily readable features, both highly dependent on the blank areas of paper substrates that form a visually integral part of all paper objects. Most paper objects are classed moderately to highly light-sensitive, but this primarily concerns media. With the exception of lignin-rich and optically brightened types, white paper, by far the most dominant material in all paper collections, is considered stable by guidelines, a classification we believe is too undifferentiated. This is our starting point. We investigate the aging-related color change patterns of white paper that we already know depend significantly on its key components (cellulosic base with salts of calcium, iron ions, gelatin, alum, lignin, optical brightening agents). We profile component-dependent, light-induced aging of new and pre-aged white paper types by their color evolution to generate a predictive model of their future light responsivity. The developed samples serve our investigation of microfading testing (MFT). MFT is currently the only available tool for in situ dose-response testing on cultural heritage. Because MFT finds increasing use in paper collections, this raises a fundamental and yet unanswered question: can the established MFT (Xenon source) and a promising new MFT (LED source) be considered appropriate tools to determine the light responsivity of white paper, and is one of the two instruments better suited for this task spectrally as well as operationally? We will clarify the significance of MFT for use on paper objects, optimize the working parameters of MFT in general and specifically its interpretability concerning paper objects and create a differentiated understanding of light-induced color change patterns in white paper. This will allow us to formulate MFT guidelines for users who are working with paper-based collections. This applied science project brings together experienced researchers, the to-date only German MFT users (Berlin, main applicant / Dresden) and experienced paper researchers in heritage preservation (Stuttgart). Some of the partners have already published jointly on relevant topics, all share knowledge transfer experience. They now build on their mutual understanding of each other’s work and complementary expertise in their first concerted effort across three applicant institutions – museum, laboratory and university.